In the course of navigation of a ship the receiver of the radar installed thereon receives radar echoes from surface objects, which may present danger to the navigator's ship, and from the sea surface and hydrometeors as well.
Clutter in the form of unwanted echoes from the sea surface and hydrometeors adversely affects the stability of automatic target tracking in the collision avoidance system. Echoes from the sea surface and hydrometeors, in the case of high sea and intensive formation of the hydrometeors, become comparable in size with the target echoes. As a result, the collision avoidance system operates to detect spurious signals and masks true target echoes. Consequently, instead of the true target the system tracks clutter signals. The probability of the selection of the spurious signals depends on the clutter intensity, the established size of the tracking gate wherein the useful signals are detected, and on the adopted target detection criterion.